SAW-US, A Build Diary

[Sportball]

It works, I connected it all up today on a temporary chassis and apart from some channel reversing it was fine. The only issue I have is that it doesn't drive in a straight line, not sure if this is a bent chassis or one wheel is running faster...any ideas?

I am also at around 175g even with a card top and no weapon. I am thinking of losing the recievers case, using cable ties instead of motor mounts and sourcing lighter wheels. I didn't realise how tough it was to be that light.

I now need to get on CAD to get the real chassis ironed out.

[joey_picus]

Which materials are you using? I'm trying to work out where the extra weight is coming from as your design looks good, but not like something that *should* be weighing that much unless you have very thick sides!

Losing the reciever's case is usually a good idea for simplicity's sake if nothing else - you could also remove the pins from the reciever, remove the connectors from the R/C cables and just solder directly to the reciever board, but as a weight saving measure it's of more use when you're two or three grams over than 25...lighter wheels might help, and if you can I would lose the metal caster as that will probably take up a fair bit of weight (the arena floors are flat enough that you don't really need to worry much about grounding yourself unless you have less than a millimetre of clearance). I would advise against losing the mounts though because of how much easier they make design, although if you're good with CAD (read: better than me) you can probably incorporate a decent, lightweight mounting mechanism into the chassis itself, so...*scales gesture*

Hope that wordspill somehow helps

[Sportball]

Hi Joey, I had another look and my temporary chassis measures 120 x 150 so a little oversize. The chassis is 1mm ALU with a 2mm display board top. Once I have my final design worked out I may switch to polycarbonate. I didn't realise how tough it is getting to weight.

[BeligerAnt]

Getting within the size limit will help with getting in weight
Those wheels are quite heavy, much lighter ones are available. You can also safely lose the caster, it's not necessary at this weight.
The best approach is to weigh all the bits individually then attack the heaviest ones first. No point in trying to halve the weight of your battery when it weighs less than 10g to start with.
A 1mm aluminium chassis should be possible within the weight, but really isn't necessary. Plastics are much lighter and work perfectly well at this size.

Good luck!

[peterwaller]

On the point about driving straight this can be caused by various problems.
Usually it is down to setting up the trims correctly.
Most speed controllers have a dead zone in the middle so the motors dont keep creeping with the stick centred so just trimming the transmitter so both motors are stopped isn't always good enough.
What you need to do is set the trims so both motors are stopped then gradullay feed in a little foward stick and check that both motors start to move at the same time. If the left motor starts first add a little left trim on the steering until both start together.
If that isn't the problem make sure that both wheels are free and cant rub on the chassis or body.

[Sportball]

Thanks for the advice, I must admit the wheels are a bit overkill but they fit perfectly on the motor shafts and appear to gave a lot of grip, I would hate to have to replace them with a bottletop or such like. Let's do a full weigh in and see how we get on.

I will have a play with the trimming and see if that will give me a straight line drive.

Thanks again..

[Sportball]

I have decided to amend the title of this post to "A Build Diary", this way I can keep all the posts in one place and anyone interested can follow.

Saw-Us is now at prototype MK2. I have ordered and received my weapon servo, a GWS PARK HPX F, after reading a recommendation. Lucky thing was it arrived in a plastic box approx 110mm x 300mm. With a little modification this box has become the shell, I am a little oversize on the width and weigh in at around 175g but it is a step in the right direction.

I have a question regarding the weapon servo. I have connected it via a live mains feed direct from the battery with the neutral and signal coming from the receiver but it is causing strange behaviour in my drive motors. Quite often after, operating the flipper, the motors spin on there own making the robot either drive backward or go into a spin. When I operate the flipper again they stop and I gain control. It appears to happen more if I drive forward and operate the flipper at the same time. I have a mode 2 Spectrum DX5e and the motors are driven via the right stick whilst the flipper is forward / backward on the left stick....any ideas.

PS photo to follow.

[BeligerAnt]

In order to diagnose the problem you may have to take a few steps backwards.
Is your battery fully charged?
If you disconnect the servo completely does the robot behave?
Even if you twiddle the left stick?
If you connect the servo to the receiver in the normal way (all 3 wires) do the motors behave?
With the servo connected how you want it, does it behave if you operate the flipper only whilst stationary?

It doesn't sound as if you have anything unusual in your setup, so it should work eventually...

[Sportball]

I will do some more investigation and let you know. In the meantime please see some photos:

[Sportball]

In order to diagnose the problem you may have to take a few steps backwards.
Is your battery fully charged?
If you disconnect the servo completely does the robot behave?
Even if you twiddle the left stick?
If you connect the servo to the receiver in the normal way (all 3 wires) do the motors behave?
With the servo connected how you want it, does it behave if you operate the flipper only whilst stationary?

It doesn't sound as if you have anything unusual in your setup, so it should work eventually...

Hi Gary, I had another play and could it be something as simple as the batteries running down? By adding the servo it obviously drains the batteries quicker than when is was motors alone, the problem only starts after around 15mins of operation. When I disconnect the servo the motors behave. I have tried connecting the servo direct to the reciever but it makes the ESC led flash as I guess it is drawing too much current.